The present invention relates to an air bag which expands to develop in accordance with inflow of gas, and particularly to an air bag and an air bag apparatus which is applied to an automobile.
Conventionally, for example, in order to protect an occupant of an automobile from an impact, there has been employed an air bag apparatus which introduces gas discharged from an inflator into an air bag so as to expand to unfold the air bag. Further, for example, an outer peripheral portion of two base cloths is sewed by means of a sewing thread, thus forming the air bag in a bag shape. Further, a so-called pyro-type inflator structured such that a gas-producing agent is quickly reacted and gas is injected into the air bag is employed for the inflator, whereby a high temperature and high-pressure gas is injected.
As mentioned above, in an air bag manufactured by sewing, when the inflator is operated, a tensile force by which the air bag expands to unfold is applied to the sewed portion in the outer periphery of the air bag, and the sewing thread is exposed to the high-temperature gas. In particular, with respect to an air bag for a driver""s seat and an air bag for a front passenger""s seat in which a tether for restricting the unfolding shape of the air bag and a partition wall for separating an interior portion of the air bag into a plurality of chambers are provided, or a side air bag developing from a side portion of the seat, or a curtain-type air bag for protecting a head portion and the like, it is hard to perform a turning inside-out operation after the air bag is sewed, so that a structure which is not turned inside out after the base cloths are sewed is employed. Then, in this structure, the sewing thread of the air bag is largely exposed at a time when the air bag is expanded to unfold and is directly exposed to the high temperature gas which is discharged from the inflator. Further, for example, since the gas generated from the inflator is injected toward a specially defined direction in the side air bag shown in Japanese Patent Application Laid-Open (JP-A) No. 9-164899, the sewing thread of the sewed portion in the specially defined area is readily affected by the heat.
Accordingly, it is necessary to work out a countermeasure against the heat, for example, or else it will be necessary to reduce the capacity of the inflator. Otherwise, it is necessary to use a sewing thread having a high heat resistance or to sew the sewing thread at twice or three times, when forming the sewed portion, which increases the manufacturing cost of the air bag.
An object of the present invention thus is to provide an air bag in which heat resistance of a sewed portion can be improved by a simple structure.
To achieve the object, a first aspect of the invention is provided with an air bag including features as follows. A bag includes a first base cloth having a first edge portion, a second base cloth having a second edge portion, and an inner space defined by the first and second base cloths. A sewing thread is used for joining the first edge portion and the second edge portion. A third base cloth is joined with the first edge portion and the second edge portion by the sewing thread. The third, base cloth has an inner edge portion extending to the inner space for covering the sewing thread.
Preferably, the third base cloth is integrally formed with a fourth base cloth which separates the inner space into a plurality of chambers.
Preferably, the first edge portion and the second edge portion are positioned outside the bag.
Preferably, the third base cloth is positioned in opposition to an inflator, so that the third base cloth is directly exposed to the gas from the inflator.
Preferably, the air bag is a side air bag which is positioned at a side portion of an automobile seat to expand to unfold.
Preferably, the bag comprises a fourth base cloth which separates the inner space into a thorax protection portion and a head protection portion, and the fourth base cloth is integrally formed with the third base cloth.
A second aspect of the invention is provided with an air bag, apparatus including features as follows. An inflator provides discharging gas and a bag accommodates the inflator filled with the discharged gas. A sewing thread joins a portion adjacent to a peripheral edge of the bag. A protection cloth is interposed between the inflator and the sewing thread for protecting the sewing thread from the discharged gas.
Preferably, the protection cloth is sewed by the sewing thread with the bag, and the protection cloth flaps inside the bag.
Preferably, the air bag apparatus further includes an intermediate cloth which separates an inner space of the bag into a plurality of chambers. The protection cloth is integrally formed with the intermediate cloth.
Preferably, the bag has an edge portion sewed by the sewing thread, and the edge portion is positioned outside the bag.
Preferably, the protection cloth is positioned in opposition to the inflator, so that the protection cloth is directly exposed to the gas from the inflator.
Preferably, the air bag apparatus is a side air bag apparatus which is positioned at a side portion of an automobile seat and to expand and unfold.
Preferably, the bag includes an intermediate cloth which separates an inner space of the bag into a thorax protection portion and a head protection portion, and the intermediate cloth is integrally formed with the protection cloth.
In accordance with the invention mentioned above, a third base cloth or a protection cloth prevents a sewing thread from being exposed to an inner space of the air bag, whereby heat resistance of the sewing portion is improved. Because the third base cloth or the protection cloth is joined by the sewing thread, a simple structure can be obtained and manufacturing cost can be reduced.
Because the fourth base cloth or the intermediate cloth is integrally formed, the number of parts can be reduced, a simple structure can be obtained and manufacturing cost can be reduced.
With respect to an air bag which is not turned inside out after the sewed portion is formed, the sewing thread is prevented from being exposed to the inner space of the air bag, whereby heat resistance of the sewing portion is improved.
Due to the preferable arrangement of the third base cloth or the protection cloth, the heat resistance of the needed portion can be improved.
Thus, the heat resistance of a side air bag can be improved and manufacturing cost can be reduced.